Process of hardening cellulose paper board with certain alums and polyhydroxyl loweralkanols and products produced therefrom



United States Patent 3,183,055 PROCESS OF HARDENING CELLULOSE PAPERBOARD WITH CERTAIN ALUMS AND POLYHY- DROXYL LOWER ALKANOLS AND PRODUCTSPRODUCED THEREFROM Leonard Mackles, 635 E. 14th St., New York, N.Y. NoDrawing. Filed May 15, 1961, Ser. No. 116,227 6 Claims. (Cl. 8--116)This invention relates to a method for preparing a treated novelhardened paper board from untreated paper board as well as to the novelproduct obtained by the process.

There are innumerable patents and procedures for fireproofing,water-proofing, insect-proofing, coating, hardening, etc., paper andpaper products to produce specifically desired results. Clearly thefield is a crowded one wherein the room for improvement is usually amatter of degree of improvement over the prior art.

Less commonly are changes made in kind wherein a novel departure fromprior art thinking and practice is revealed.

The specific improvement of this invention is an improvement over theprior art both in degree and in kind as will be described hereinafter.

A greatly desired result in the box board and allied fields is thepreparation of corrugated paper board having about the crush strengthof, for example, sheet steel. Were such a board possible, the packagingof mechandise and the shipping of it great distances would be done withgreat safety from damage due to the boxes being broken or mutilated bythe rough handling normally associated with freight transportation.

Attempts have been made to harden corrugated paper board by the use ofinorganic salts, for example, am- 3 monium alum Al (SO .(NH (SO ).24H Obut the results have been unsatisfactory. Generally the alum is dilutedwith water and the paper board is immersed therein for a relativelyshort time by a dipping procedure. The results of such dipping gaveerratic results probably due to the uneven absorption of the waterrelative to the absorption of the dissolved ammonium alum molecule bythe paper at its planar surface and at the interface between the liquidsolution and the atmosphere.

In any event the process is not commercially feasible because the waterand the alum are not uniformly and consistently absorbed by the paperboard in the ratio present in solution. The coated dried board insteadof having a uniformly hard planar coating and thus yield uniform testreadings had in fact a most non-uniform coating having areas of extremehardness intermingled among areas of extreme weakness.

This problem of erratic results puzzled the art and the solution of itwas urgent.

It is an object of this invention to provide a coat-hardened fibrousboard having a uniformly hard coating chemically bonded to a fibrouscellulosic board.

'It is another object to provide a hardened corrugated paper board ofexceptional strength.

It is a further object to provide a hardened coated paper board havingincreased resistence to fire.

It is another object to provide a commercially feasible method forproducing a uniformly hardened fibrous board.

It is a further object to provide an inexpensive method for obtaining asuperiorly hardened paper board.

These and still other objects of this invention will become apparentupon reading the following descriptive disclosure taken in conjunctionwith a plurality of illustrative examples, illustrating the wideversatility of the invent both as to its application to industry and asto the ingredients employed.

3,183,055 Patented May 11, 1965 According to this invention ammoniumalum and potassium alum (Al SO .K SO 24H O are used to accomplish thedesired result, in conjunction with the use of a polyalcohol compound. 7

According to this invention the use of polyalcohols, also calledpolyhydroxyalcohols, in lieu of water in preparing the ammonium alum orthe potassium alum solution results in a process yielding rapid andstablized impregnation of the alum into the cellulosic fibrous material.The product obtained by this invention has a uniform hard coatingthereon which is believed to be chemically bonded to the cellulosicmolecules.

Contrary to the irregular surface of the dried paper board obtained whenammonium alum dissolved in water is used, the paper board obtained whena polyhydroxyl compound is used as the solvent to make the ammonium alumsolution has a smooth glossy surface.

Moreover, the coating obtained on corrugated paper board when using theprior art aqueous solution of ammonium alum is relatively easily priedaway from the paper base; but when, for example, a glycol or otherpolyhydroxyl alcohol is used as the solvent, the coating is stronglybonded to the cellulosic material in a chemical manner so that thecoating is believed to be integral with the cellulose moleculesconstituting the surface of the paper board.

Moreover, because of the presence of the high molecular weightpolyhydroxy alcohol unit in the coating absorbed on the paper surface,the hardened coating obtained by drying, yields an over-all productwhich is excessively resistent to fire. Clearly a high molecular weighthigh boiling liquid is a better fire retardant than the relative easilyvolatilized water molecules of the prior art products.

Furthermore, the use of glycols and other polyhydroxyl alcohols effectsa rapid wetting of the cellulosic material. Besides, unlike the soggyand limp paper product obtained when a corrugated paper board sheet isdipped in an aqueous solution of alum for any prolonged time, the.

use of a polyhydroxyl alcohol as a solvent for the ammonium alumsolution permits a long residence time or absorption time withoutproducing a limp and soggy paperboard. In short, the water of an aqueousalum solution dissolves the aqueous adhesive used in the manufacture ofconventional corrugated board. But the high molecular weightpolyhydroxyl alcohol solvent do not appreciably dissolve the watersoluble adhesives customarily used in making corrugated paper board.

Ammonium alum and potassium alum have high melting points, so that whenmolten alum solutions are employed the water of hydration is easilydriven off and in the prior art it was often condensed and returned tothe aqueous solution to keep the solution suitably thin or viscous, lestit become too thick for convenient dipping and absorption of coating bythe paper stock being used.

However,-where high boiling point polyhydroxyl alcohols are used inplace of water as the solvent, the danger of driving off the solvent atthe high temperatures employed of F. to 210 are very small, so that lessmanual care need be applied to this process making it a relativelyinexpensive self-regulating process.

Experience obtained in making many varities of hardened cellulosic paperboard leads to the belief that the polyhydroxyl alcohol when used as asolvent is substituted I has its water molecules replaced in whole or insubstan tial part by glycol molecules.

Moreover, when such an ammonium alum solution having glycol molecules inlieu of water molecules is heated to the temperatures employed in thisinvention, namely 180 F. to 210 F. and a cellulose containing board isdipped therein, it is believed that the hydroxyl group on the compoundsreact with the hydroxyl groups present in cellulose to form anether-like linkage. Such chemical bonding is impossible where aqueoussolutions of alum are employed.

In this invention a large number of polyhydroxyl alcohols are operableas solvents since they are miscible with the alum at the hightemperatures employed. Thus ethylene glycol is operable and a preferredsolvent. Similarly I also prefer to use propylene glycol and glycerol.Moreover, I have tried hexylene glycol, trimethylene glycol, triethyleneglycol and diethylene glycol and found them to be operable. In short,there is a vast number of operable polyhydroxy alcohols which may besubstituted for the water of hydration in ammonium alum and yieldadvantageous results in that a superior paper board product is obtained.

Two tests were performed on the paper stock used. The paper stock usedwas, (a) 350 Mullen Test double wall corrugated paper board and (b) 200Mullen Test single wall corrugated paper board. Specimens of arectangular shape having the dimensions of six inches by fourteen incheswere used for a hardness test and for a crush test.

The hardness test consisted of placing the paper board on a pair ofparallel disposed knife-like edges disposed 12 inches apart so that theboard over-lapped each knife edge by one inch. A plurality of discweights of four inches in diameter weighing five pounds each wereassembled.

The untreated or blank 350 Mullen Test corrugated paper board broke onthe application of fifty pounds of weights at the center area locatedbetween the two knife edges. In the case of the untreated or blank 200Mullen Test single wall paper board the specimen broke, i.e. caved in,upon the application of thirty-five pounds of weight in its center.

Another test was made to see how the flutes stand upon the addition ofthe five pounds weight. This test was a crush test for testing the forcenecessary to crush the flutes of the above two types of corrugated paperboard used.

In the case of the untreated 350 Mullen Test corrugated paper board, itwas noted that with the paper board disposed on a flat horizontalsurface a load of fifty pounds on a four inch diameter area saggedflutes fifty percent of their original height.

Where 200 Mullen Test single wall untreated paper board was used a loadof fifty pounds on a four inch diameter center crushed the flutessubstantially completely.

The following examples of this invention illustrates its wide varietyand scope.

In all examples used herein, the test specimens of 350 Mullen doublewall corrugated paper board and of 200 Mullen single wall paper boardwere six by fourteen inches in size. And all tests were performed atnormal room temperature and humidity conditions.

Example 1 Nine parts by weight i.e. nine pounds of potassium alum andten parts by weight i.e. ten pounds of ethylene glycol were poured intoa container and the mixture was heated carefully to 190 F. to 195 F. Asix inch by fourteen inch sheet of conventional 350 Mullen Test doublewall corrugated paper board was immersed in this solution for a periodof ten seconds after which it was removed and air dried at roomtemperature. This treated board was tested for its hardness using saidfive pounds disc weights such as are used in weight lifting devices.This board did not break even upon the application of two hundred poundson a four inch area located at the center of the specimen.

Clearly a marked improvement over the untreated board that broke uponthe application of a fifty pounds load is apparent.

A crush test was performed on this double wall board using the pluralityof five pounds weights upon an above treated dried corrugated paperboard and no visible sagging of the flutes was noted even upon theapplication of two hundred pounds of weight on a four inch diameterarea. The untreated double wall board showed a fifty percent sagging offlutes with a load of fifty pounds.

Where 200 Mullen single wall paper board was immersed for five secondsin the potassium alum bath at to F. and then dried, the hardness testshowed no break even after addition of five pound weights to a total ofone hundred pounds. In this case the crush test showed no visible flutesagging even after the addition of weights to a total force of onehundred eighty-five pounds.

The treated potassium alum paper boards of both the 350 Mullen Test andof the 200 Mullen Test specimens were then subjected to flame tests tosee if they would sustain a flame. Neither specimen sustained a flame.

The treated product for both the 350 Mullen Test and the 200 Mullen Testspecimens were smoothly coated and had a stone hard surface.

Example II The procedure of Example I was repeated exactly as describedtherein but using 9 parts of ammonium alum in lieu of the nine parts ofpotassium alum to see what the effect would be. It was learned that thehardness test of the 350 Mullen double wall paper board obtained by theuse of ammonium alum also did not break at the application of a twohundred pound load. In the case of the ammonium alum treated 200 MullenTest single wall paper board a test for hardness showed no break evenafter one hundred pounds or weights were added.

In the crush test of the treated ammonium alum specimens, a 360 Mullendouble wall specimen withstood a two hundred pound load without visiblesign of crushing of flutes and the 200 Mullen single all specimenwithstood a one hundred eighty-five pounds load without a sign ofvisible crushing. I

All the ammonium alum specimens also exhibited a smooth uniformly coatedhigh gloss hard coating as in the case of the potassium alum-ethyleneglycol mixture.

Example III The procedure of Example I was repeated but using a refluxcondenser to return any Water of hydration which may have evaporatedduring the heating and dipping operation. It was noted that the treateddouble wall corrugated paper stock and the treated single wallcorrugated paper stock gave substantially identical hardness and crushtests as when no provision is made to return the water of hydration tothe container of the solution.

Accordingly it was believed that the return of the water of hydrationassociated with the alum was immaterial to obtain an improved product solong as a substantial amount of polyhydroxyl alcohol was present.

Example IV board hardness test showed no bending at the application of aone hundred pound load and the crush test showed no visible flutesageven on the application of a one hundred eighty-five pound load.

Example V The procedure of above Example IV using propylene glycol wasrepeated using nine parts of ammonium alum in place of the nine parts ofpotassium alum and using a thirty second immersion time in lieu of tenseconds. The results of this experiment were as follows:

The double wall corrugated specimen gave a hardness test of no bendingeven with a load of two hundred pounds.

The coated and air dried single wall corrugated paper board gave ahardness test of no bending even with a two hundred pound load and thesingle wall coated and dried paper board exhibited no bending even witha one hundred pound load. Also the crush test of the propylene glycolammonium alum double wall coated corrugated specimen showed no visibleflute sag upon the application of a two hundred pound load in the crushtest. The single wall corrugated board treated with propylene glycol andammonium alum showed no visible crush of flutes in the crush test evenupon the addition of a one hundred eighty-five pound load.

The tests using nine parts of ammonium alum were repeated with one parthexylene glycol (molecular weight 118.18) for a ten second immersiontime. The results with the coated double wall corrugated paper boardwere as follows:

No bending in the hardness test was noticeable upon applying a load oftwo hundred pounds. No crushing of flutes even with a two hundred poundload on a four inch diameter area, was observed.

Triethylene glycol (molecular weight 150.18) was then substituted forethylene glycol in Example I.

The double wall corrugated paper board showed a noticeable sag in thehardness test.

Also the single wall corrugated paper board coated with nine partsammonium alum using one part triethylene glycol onhardness testingshowed a visible sag.

It was concluded that in the preparation of the hard coating of thisinvention, the lower molecular weight glycols and polyhydroxy alcoholswere preferred and particularly propylene glycol and ethylene glycol.

This invention is of generic scope as to the time of immersion of thecellulosic material into the molten bath. The preferred range ofimmersion time is fromabout ten seconds to about forty seconds, butlonger immersion times is operable and clearly where a longer immersiontime is employed the amount of coating on the cellulosic material isgreater. The operable temperature range is from about F. to about 210 F.but a range of about F. to about 210 F. is preferred and the optimumrange desired is from about F. to 200 F.

This invention has been described by means of several embodiments but itis not limited thereto as the weight of the ingredients may be variedfrom the nine parts of alum to one part of polyhydroxyl alcohol to nineparts of alum (ammonium or potassium) to about one-half partpolyhydroxyl alcohol or lessto about three parts said alcohol or more.The amount of polyhydroxy alcohol to be used is determined in part bythe cost thereof since such alcohols are relatively expensive. Moreovermixtures of the polyhydroxyl alcohols are operable. Accordingly thescope of this invention is limited only by the claims herein.

I claim:

1. A process of preparing a hard coating on a cellulose paper boardcomprising preparing a molten mixture of about nine parts by weight ofalum selected from the group consisting of ammonium alum and potassiumalum with about one-half to about three parts by weight of solvent, lowmolecular weight, liquid, non-substituted,

polyhydroxyl lower alkanols, maintaining said molten mixture at atemperature between 170 F. to 210 F., immersing said paper board in saidbath for about ten to about forty seconds time interval and thereafterremoving and air drying said coated paper board to obtain a smooth alumcoating bonded to said cellulose paper board.

2. The process of claim 1 wherein the temperature range 1 of the moltenbath is from about 185 F. to about 210 3. The process of claim 2 whereinthe time of immersion of said paper board is from about ten seconds toabout thirty seconds.

4. The process of claim 1 wherein the polyhydroxyl alkanol is selectedfrom the group consisting of ethylene glycol, propylene glycol andglycerol.

5. The product prepared by the process of claim 1.

6. The product prepared by the process of claim 4.

OTHER REFERENCES Chem. Abst., vol. 54, 1960, p. 18957 (b). Chem. Abst.,vol. 54, 1960, p. 25822(a).

NORMAN G. TORCHIN, Primary Examiner.

1. A PROCESS OF PREPARING A HARD COATING ON A CELLULOSE PAPER BOARDCOMPRISING PREPARING A MOLTEN MIXTURE OF ABOUT NINE PARTS BY WEIGHT OFALUM SELECTED FROM THE GROUP CONSISTING OF AMMONIUM ALUM AND POTASSIUMALUM WITH ABOUT ONE-HALF TO ABOUT THREE PARTS BY WEIGHT OF SOLVENT, LOWMOLECULAR WEIGHT, LIQUID, NON-SUBSTITUTED, POLYHYDROXYL LOWER ALKNOLS,MAINTAINING SAID MOLTEN MIXTURE AT A TEMPERATURE BETWEEN 170*F. TO210*F., IMMERSING SAID PAPER BOARD IN SAID BATH FOR ABOUT TEN TO ABOUTFORTY SECONDS TIME INTERVAL AND THEREAFTER REMOVING AND AIR DRYING SAIDCOATED PAPER BOARD TO OBTAIN A SMOOTH ALUM COATING BONDED TO SAIDCELLULOSE PAPER BOARD.